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chromium
Columbia Encyclopedia entry: chromium
Chromiumkrō'mēəm [Gr.,=color], metallic chemical element; symbol Cr; at. no. 24; at. wt. 51.996; m.p. about 1,857°C; b.p. 2,672°C; sp. gr. about 7.2 at 20°C; valence +2, +3, +6. Chromium is a silver-gray, lustrous, brittle, hard metal that can be highly polished. It is found in Group 6 of the periodic table. It does not tarnish in air, but burns when heated, forming the green chromic oxide. When combined with oxygen, besides yielding chromic oxide, which is used as a pigment, it forms chromic anhydride (the red trioxide and anhydride of chromic acid). With other metallic elements, e.g., lead and potassium, together with oxygen, it forms the chromates and dichromates. These compounds are salts of chromic acid and are used as pigments in paints, in dyeing, and in the tanning of leather. Chrome yellow, a pigment, consists largely of lead chromate. Other chrome colors are black, red, orange, and green. In the chrome process for tanning leather, a dichromate is used, and chromium hydroxide, a basic compound of chromium, hydrogen, and oxygen, is precipitated and held in the leather. The hydroxide is used also as a mordant in dyeing cloth. A mixture of potassium dichromate and sulfuric acid is used as a powerful agent for cleaning laboratory glassware. Chromium is a comparatively rare element, never occurring by itself in nature but always in compounds. Its chief source is the mineral chromite, which is composed of iron, chromium, and oxygen and is found principally in the nations of the former Soviet Union, South Africa, Zimbabwe, Turkey, and the Philippines. The element, in the form of chromic oxide, gives the greenish tint to the emerald and the aquamarine. Metallic chromium is prepared by reduction of the oxide by aluminum or by carbon. It is used in plating other metals because of its hardness and nontarnishing properties. In alloys with other metals it contributes hardness, strength, and heat resistance. Its most important use is in the steel industry, where it is a constituent of several alloy steels, e.g., chromium steel or chrome steel. Stainless steel contains from 11% to 18% chromium. An alloy of nickel and chromium, often called Nichrome, is widely used as a heating element in electric toasters, coffeepots, and other appliances. Stellite is an extremely hard alloy of cobalt, chromium, and tungsten, with small amounts of iron, silicon, and carbon; it is used in metal cutting tools and for wear-resistant surfaces. A similar alloy, with molybdenum instead of tungsten, is used in surgical tools since it does not react with body fluids. Chromium was discovered in 1797 by L. N. Vauquelin.

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Wikipedia search results for: Chromium
From Wikipedia, the free encyclopedia
Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma", meaning color, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin in the mineral crocoite in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well. Chromium was regarded with great...more »
Columbia Encyclopedia search results: chromium
Results 1 - 10  of 47
  • Periodic Table of the Elements: Chromium

    Periodic Table of the Elements: ChromiumAtomic Number:24Atomic Symbol:CrChromiumAtomic Weight:51.996ElectronConfiguration:2 · 8 · 13 · 1

  • Cr

    Cr, symbol for the element chromium.

  • Sierra Maestra

    Sierra Maestra, rugged mountain range, SE Cuba, rising abruptly from the coast. Consisting of connecting ranges with local names, the Sierra Maestra is the highest system of Cuba. It is rich i...

  • emerald

    Emerald, the green variety of beryl, of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The ...

  • tape recorder

    Tape recorder, device for recording information on strips of plastic tape (usually polyester) that are coated with fine particles of a magnetic substance, usually an oxide of iron, cobalt, or ...

  • Thetford Mines

    Thetford Mines, city (1991 pop. 17,273), S Que., Canada, NE of Sherbrooke and S of Quebec. The city, developed after the discovery (1876) of large asbestos deposits, is located in one of the w...

  • Aqtöbe

    Aqtöbe or Aktöbe, formerly Aktyubinsk, city (1993 est. pop. 264,000), NW Kazakhstan, on the Ilek River and the Kazalinsk RR. Aqtöbe has an important ferroalloy plant and chromium complex based...

  • Kütahya

    Kütahya, city (1990 pop. 131,286), capital of Kütahya prov., W central Turkey. An agricultural market center producing sugar beets, fruit, and cotton. Iron, lignite, mercury, and chromium are ...

  • Tarsus

    Tarsus, city (1990 pop. 191,333), S Turkey, in Cilicia, on the Tarsus (anc. Cydnus) River, near the Mediterranean Sea. It is an agricultural trade center; copper, zinc, chromium, and coal are ...

  • alum

    Alum, any one of a series of isomorphous double salts that are hydrated sulfates of a univalent cation (e.g., potassium, sodium, ammonium, cesium, or thallium) and a trivalent cation (e.g., al...

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